9/16/13 1 Chapter 13 How cells obtain energy from food Be Able To • Compare/contrast oxidative phosphorylation and substrate-level phosphorylation, including the location of the reaction, the molecules involved and the mechanism of energy transfer to ATP. • Identify the location for glycolysis, fermentation, citric acid cycle and oxidative phosphorylation. • Compare/contrast cellular respiration and fermentation. • Describe the flow of metabolites (including their electrons) during glycolysis and the citric acid cycle. Which activated carrier molecules are involved? What is their relative energy yields? • Describe the role for hexokinase, phosphofructokinase, aldolase and pyruvate kinase in glycolysis. • Explain the role of Acetyl-CoA and pyruvate dehydrogenase complex. • Identify the processes that result in CO2 production.9/16/13 2 The breakdown and oxidation of food occurs in three stages ?9/16/13 3 Glycolysis Conversion of glucose (6C) to two molecules of pyruvate (3C) 10 enzymatic steps (harvest energy in small steps) All steps occur in the cytosol ATP production: Requires an initial investment of two ATP Produce four ATP Net yield => two ATP No O2 involved, but oxidation of an intermediate occurs (NAD+ → NADH) Yields two NADH per glucose NADH and NADPH are electron carriers A + e- + H+ → AH Review chapter 39/16/13 4 Glycolysis Glycolysis - Energy Investment Steps9/16/13 5 Glycolysis - cleavage from 6C to 3C Glycolysis - First energy producing steps These reactions are coupled to yield NADH and ATP Substrate-level phosphorylation9/16/13 6 Substrate-level phosphorylation Production of ATP by direct transfer of a high-energy phosphate group to ADP Substrate-level phosphorylation9/16/13 7 Glycolysis - Second energy producing steps Also substrate-level phosphorylation9/16/13 8 Glycolysis What happens to pyruvate?9/16/13 9 Fate of pyruvate under anaerobic conditions Muscle cells Fate of pyruvate under anaerobic conditions Yeast cells9/16/13 10 Fate of pyruvate under aerobic conditions Pyruvate is transported into the mitochondria where it is oxidized to acetyl CoA and CO2 by a large, 3-enzyme complex: pyruvate dehydrogenase complex Activated carriers Coenzyme A, Acetyl CoA9/16/13 11 In eukaryotic cells, acetyl CoA is produced in mitochondria What about prokaryotic cells? Citric acid cycle Pyruvate dehydrogenase Electron transport ATP synthase Permeability barrier Porins Mitochondrial compartments9/16/13 12 Citric Acid Cycle Complete oxidation of the acetyl group of acetyl CoA to CO2 8 enzymatic steps (harvest energy in small steps) In eukaryotic cells, all steps occur in the mitochondrion Mitochondrial matrix High energy yield: 1 GTP 1 FADH2 3 NADH Does not use O2 directly, but requires O2 to regenerate NAD+ Citric Acid Cycle Citrate synthase9/16/13 13 GTP is an activated carrier that is readily converted to ATP GTP + ADP ⇔ GDP + ATP Nucleoside diphosphokinase FADH2 is an electron carrier The electrons have slightly lower energy than those held by NADH9/16/13 14 Energy released during passage of electrons through the electron-transport chain is harnessed to pump protons across the mitochondrial inner membrane FADH2 Chemiosmotic process converts energy from electron donors into ATP9/16/13 15 The proton electrochemical gradient drives ATP synthesis This is oxidative phosphorylation compare to substrate-level phosphorylation in glycolysis9/16/13 16 Cellular respiration is the complete oxidation of food molecules, like glucose, to CO2 and H2O 1. Glycolysis + 2. Citric acid cycle + 3. Oxidative phosphorylation Oxygen is consumed by the electron-transport chain and ultimately, large amounts of ATP are produced via oxidative phosphorylation FADH2 from Citric acid cycle Final electron acceptor Electron-transport chain drives oxidative phosphorylation ~ 30 ATP per glucose Cellular respiration O2 is reduced to H2O, not released as CO29/16/13 17 Central Metabolic Pathways Review questions 13-1, 13-5, 13-10 13-11, 13-12,
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